1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a radio frequency (RF) quadrature transceiver, and more particularly, to compensating for a mismatch occurring in an RF quadrature transceiver based on a direct-conversion scheme.
2. Description of the Related Art
In digital communications using a method of modulating or demodulating a phase or a frequency, a direction conversion method not using an intermediate frequency band uses an in-phase carrier signal and a quadrature-phase carrier signal that have a phase difference of 90 degrees. However, when a phase difference between the two signals is not exactly 90 degrees, or a mismatch between the overall gains obtained by the paths of the two signals is generated, signal distortion can occur. Accordingly, research into a method of efficiently and accurately compensating for a phase mismatch and a gain mismatch has been conducted.
FIGS. 1A and 1B are schematic diagrams illustrating structures of related art radio frequency (RF) quadrature transceivers. FIG. 1A illustrates a related art radio frequency integrated circuit (RFIC) manufactured by Athena Semiconductors, Inc., in which a feedback loop is established between a transmission module and a reception module, and thus a phase mismatch and a gain mismatch are compensated for by using a predetermined algorithm after a signal transmitted by the transmission module is directly received by the reception module. However, the RFIC of FIG. 1A must include a special envelope detector in order to achieve this mismatch compensation, and the reception module must perform a complicated digital signal processing operation using a signal received via the envelope detector.
FIG. 1B illustrates a related art RFIC manufactured by Atheros Communications Inc. This RFIC employs a 2-stage conversion scheme, such that signals having a phase difference of 90 degrees are not used in an RF band and a quadrature signal is generated in a frequency band (e.g., ¼ of a carrier frequency band) lower than the RF band. Therefore, the 2-stage conversion scheme generates fewer phase errors and fewer gain errors than when employing the direct conversion scheme. However, the compensation method of FIG. 1B also cannot completely prevent generations of a phase mismatch and a gain mismatch. Rather, the use of an intermediate frequency causes an image frequency problem. Moreover, the 2-stage conversion scheme requires more mixers and more LO2 generation circuits than the other schemes. Accordingly, the RFIC employing the 2-stage conversion scheme consumes much power and has a large size.